Cervical Cancer Immunization
from Practice Update, Summer 2007
Stephen M. Scott, MD, FACOG, Chair, Pediatric and Adolescent Gynecology, The Children’s Hospital,Associate Professor, Departments of Obstetrics/Gynecology and Pediatrics, University of Colorado at Denver and Health Sciences Center
Cervical cancer continues to be a major health issue. Worldwide, over 500,000 new cases of cervical cancer are diagnosed each year and nearly 290,000 deaths occur annually. The incidences of new cancers and deaths each year in the United States are approximately 9,700 and 3,700 respectively.
Rigorous efforts to screen for cervical cancer in the United States have been successful to a point. The Pap smear has significantly reduced the incidence of cervical cancer by detecting precancerous lesions. These lesions are then removed and more intense observation is instituted to ensure there is no persistence or return of disease. Unfortunately, this shift in management has its own price. The annual cost of surveillance and treatment of precancerous lesions is $3.6 billion in the United States alone. Until recently, treatments required destruction of large areas of cervical tissue, which can have immediate post operative complications and subsequently lead to increased rates of infertility, miscarriage and low birth weight infants during future pregnancies.
We now know that persistent HPV infections are the causative agents in developing cervical pre-cancer and cancer lesions. HPV is so prevalent within the human population that the question of infection among sexually active people is not so much “if”, but “when” an infection will occur. By 50 years of age, at least 80 percent of women will have acquired a genital HPV infection. Three quarters of new infections will occur in younger adults ages 15 to 24.
Avoiding high-risk behavior does not prevent HPV infections. Two similar studies found HPV infections in 45 percent of young women three years after initiating sexual intercourse and maintaining mutual monogamy. We know that cervical cancer is caused by high-risk HPV subtypes. Persistent infections, from types 16 and 18, account for almost 70 percent of cervical cancers. Genital warts arise from persistent low-risk HPV subtypes. HPV types 6 and 11 account for over 90 percent of genital wart infections.
Unfortunately, we are unable to determine who will get an HPV infection, what subtype of HPV they may be infected with, and if they will be able to clear the infection and develop natural immunity. An infected person’s natural immune response relies on cell-mediated immunity and is variable and delayed in its response to HPV infections.
The introduction of HPV vaccination has provided an advance in the treatment of cervical cancer. We now can prevent a majority of genital warts, pre-cancer and cancer lesions from ever developing instead of relying on monitoring and destructive treatments. The vaccine uses a noninfectious protein from the HPV capsule to stimulate a more vigorous humoral immune response. Currently, a quadrivalent vaccine for types 6, 11, 16 and 18 is available. A bivalent vaccine, covering type 16 and 18, will be available in the future. To complete the vaccine series, required injections begin at the time of the decision to treat, followed by another injection after two months and again at six months.
The vaccine is very effective when given prior to exposure to these HPV types. Ninety-eight percent efficacy was seen in preventing moderate to severe cervical dysplasia caused by types 16 and 18; and 99 percent efficacy in preventing genital warts from all four types was noted in women ages 16 to 26 who had not been infected with these HPV types prior to or during the vaccination phase. The vaccine is not effective for a type that has already infected a patient. There is still efficacy against any remaining types that a person has not been exposed to.
The study population noted that 93 percent of patients had none or only one of the four HPV types regardless of sexual activity. Therefore, the FDA currently recommends vaccinating up to age 26 without regard to past or present activity. Additional studies found that the immune response was more intense in adolescents under the study age group. This vigorous immune response is thought to provide the same or better protection. Because the vaccine is most effective prior to HPV exposure, the FDA approved vaccination for all females ages 9 to 26 with a focus on 11 to 12-year-olds.
The adverse events noted after HPV vaccinations are similar to other vaccines given in childhood and adolescence. The vaccine is a pregnancy Category B drug. It should not be given in a known pregnancy, but should not effect decisions made about a pregnancy if it is given inadvertently. Completion of the series may resume six weeks postpartum even if the patient if breastfeeding. The vaccine can be given at the same time as other vaccines. Recommended cervical cancer screening should not change despite vaccination. Immunocompromised patients, including HIV-positive patients, can be given the vaccine, but should be counseled that the efficacy for cancer and wart prevention is unknown.
Other preventive measures, including abstinence, mutual monogamy and condom use should be discussed with patients in conjunction with the HPV vaccine counseling.
For more information
For more information about HPV vaccinations or pediatric and adolescent gynecology at The Children’s Hospital, please contact Stephen Scott, MD at (303) 315-4540 or by email at stephen.scott@uchsc.edu. To make a pediatric/adolescent gynecology appointment with Dr. Scott, please call (303) 861-6182.
